This earthwork, while simple in its nature, is very worthwhile in several different contexts to achieve higher water quality and prevent sedimentation in other earthworks. This helps to save time and money and allow other earthworks to be more energy efficient through working with slope dynamics. The pattern behind it is more edge; that in the past beavers probably did this work but we now use machines and hand tools to slow the descent of sediments from entering into other earthworks. They are located for ease of access and the subsequent cleaning so their sediment trapping capability stays high. In disturbed landscapes, which most are these days, it is truly amazing to see just how much sediment moves and subsequently caught.
I have seen or implemented several different types of silt traps in my years of work and travel. While above I say these earthworks, they can also be man-made structures from concrete given the right context. In one such case at Terra Mae, our original development project in Portugal, there was a diversion drain across the road leading to a pipe. Instead of this pipe going straight to its final destination, a 16,000 gallon or 64,000 liter tank, it instead was piped in and out of a silt trap first. Thus the immense rain water runoff from the road laden with all sorts of sediment, but mostly sand and silts, was led from the diversion drain into a silt trap concrete box then to the water tank. Without it sedimentation would occur at a higher rate and necessitate cleaning of the tank more often. This is a very big process as we have gone through it at many sites there in Portugal. Also without the silt trap you run the risk of clogging pipes as the outlet is located towards the bottom of the tank. Furthermore it also diminishes volume capacity, which is paramount in these locations of brittle climates where rain can be sparse or non existent for five to seven months. This applies both to tanks and also earthen structures say a dam created for irrigation.
Thanks Douglas , I have been slowly trapping silt behind log and rock dams in a creek that once was buffered with beaver dams and now has places washed out to 30 ft deep. My brother and I have also been discussing a giant silt trap on his 35 acre property, so your article was very timely for us.